Angle switching device for synchronizing two synchronous motors



Oct. 10, 1939. c, c s u 2,175,923

ANGLE SWITCHING DEVICE FOR SYNCHRONIZING TWO SYNCHRONOUS MOTORS I FiledJuly 16, 1935 2 SheetsSheet 1 WITNESSES; INVENTOR fi fl C/2ar/e.sCffihulf (a ine 0M g F.

/ ATTORNEY Patented Oct. 10, 1939 UNITED STATES aus PATENT OFFICE ANGLESWITCHING DEVICE FOR SYN CHRO- NIZING TWO SYNCHRONOUS MOTORS Charles C.Shutt, East McKeesport, Pa., assignor to Westinghouse Electric &Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application July 16, 1935, Serial No. 31,614

3 Claims.

My invention relates to means for effecting a given relative operatingposition of two or more shafts which are to operate in synchronism. Moreparticularly, my invention relates to 5- electric control system wherebythe relative rotor positions at a given instant of two or more electricmotors operating in synchronism is effected. It often happens that theload characteristics, namely, the variations of torque of the loaddriven 1 by one prime mover has periodic variations. When several suchloads are to be coupled to a prime mover it is desirable that the drivenshafts be coupled to the prime mover in such relative angular relationwith reference to corresponding planes including the driven axes thatthe peak torques of all the loads do not occur at the same time.

One object of my invention is to provide for driving two or more shaftsin synchronism but in such relative relation that corresponding pointson the shafts hold selected positions with reference to correspondingplanes including said respective shafts.

The advantages of my invention are particula-rly noticeable inconjunction with the operation of a plurality of synchronous motorsdriving loads of varying character, as for instance compressors.

Synchronous motors are, as a rule, started as induction motors and at ornear synchronism transferred from induction motor operation tosynchronous motor operation. If several synchronous motors are connectedto the same source of supply, the desirable starting operation is thatall the motors are not synchronized at the same time. Furthermore, ifthe motors are coupled to loads that very periodically it is verydesirable that the peak loads on the motors do not occur at the sameinstant.

For instance, if two or more synchronous motors are to operatecompressors, it would not be desirable that the crank arms occupy thesame relation during synchronous operation. If the motors could besynchronized so that corresponding poles hold different positions at agiven instant during synchronous operation, it is apparent that the peakloads for the respective motors would occur at different times.

One object of my invention is to so synchronize a plurality ofsynchronous motors that corresponding pole pieces hold selectedpositions at a given instant during synchronous operation.

Another object of my invention is to control the successivesynchronization of a plurality of motors so that corresponding points onthe shafts of the motors hold selected angular positions at a giveninstant with reference to corresponding planes including the axes of therespective motors.

Another object of my invention is to synchronize a synchronous motor atsuch an instant that its shaft will hold a given relation to the shaftof anothersynchronous motor operating at synchronism.

A still further object of my invention is to con- 10 trol the successivesynchronization of synchronous motors by electric discharge means thatare made responsive to the relative angular disposition of the shafts ata given instant.

Other objects and advantages of my invention will become more apparentfrom a study of the following specification when taken in conjunctionwith the accompanying drawings, in which:

Figure 1 shows a starting control scheme for a synchronous motor, and aportion of the 20 combined control scheme constituting my invention; and

Fig. 2 shows, a starting control scheme for a synchronous motor, and theremaining portion of the combined control scheme constituting my 25invention.

Referring more particularly to Figs. 1 and 2 of the drawings, thereference character I'I designates a synchronous'motor which may be connected to the source of supply represented by the conductors I, 2 and 3by suitable operation of the contactor I. In the particular arrangementshown in both figures time limit control means are shown for both motorsI I and Ill]. The time limit device in Fig. 1 is represented by anelectromagnetic device I2 provided with a dashpot 53. The field windingof the motor is arranged to be connected to a pair of direct currentbuses BI and 64 by the main field switch 30 and a high speed fieldswitch 231. The high speed field switch 231 is suitably controlled bythe electric discharge device 215.

In Fig. 2, motor IIO may be similarly interconnected with the source ofalternating current represented by the conductors I, 2 and 3 by the 45contactor IU'I, a time limit device 3I2 is shown for delaying theenergization of the field winding with direct current from the directcurrent buses BI and 64 by the main field switch 45.

A high speed field switch 208 may also connect the field winding ofmotor I10 to the source of direct current when the electric dischargedevice I15 becomes conducting.

As hereinbefore pointed out in the objects, it is one of the desirablefeatures of my system of control to synchronize either one of the twomotors shown when the other is operated in synchronism at such aninstant that the shaft of the motor last to synchronize will hold adefinite relation with reference to the shaft of the motor first tosyn-chronize.

In the drawings, motor ll is provided with an impulse generator 23,whereas motor lltl is provided with an impulse generator l23. Theseimpulse generators are so arranged that their voltage impulses occur atthe same instant when certain points on the shafts of the respectivemotors hold different angular positions with reference to the axis ofthe motor shafts and corresponding points on the stators.

The impulse generators are arranged to vary the grid bias of theelectric discharge devices shown and the arrangement of the circuits issuch that the particular electric discharge device that is to be causedto operate will only operate when the voltage impulses act concurrentlyor additively.

As hereinafter explained more in detail, when one of the motors iscaused to synchronize, certain electro-magnetic devices and one of theelectric discharge devices is disconnected so that it is not utilizedfor the synchronization of the motor last to be synchronized, but thescheme of control is such that no particular order of synchronization ofthe motors need be selected. Motor llil may be started first or motor llmay be started first. If motor l'lii is started first, electricdischarge device 2l5 in Fig. l is the device utilized for controllingthe synchronization of motor ll. Furthermore, if motor ll issynchronized first, the electric discharge device lie is utilized tosynchronize motor Hi).

If motor ll is operating at synchronous speed and motor Ilil hasattained its balance speed operating as an induction motor and the timelimit device 3l2 has operated, the impulse generators will cause theoperation of the electric discharge device I15 and synchronize motori'ifl at such an instant that the peak loads on the two motors will notoccur at the same time.

A better understanding of the novel features of my invention canprobably be had from a study of typical operating sequences for the twomotors that are to be energized and synchronized in such a manner thatcorresponding pole pieces are disposed in different relation on the twomotors or what is more important that the crank arms on the shafts ofthe motor be in different operating relation.

Assuming that conductors l, 2 and 3 are suitably energized by analternator or be energized from conventional power means, and theattendant wishes to set motors ll and iii! in operation in the desiredmanner. Further, assuming for the first sequence of operation that theattendant wishes to start motor ll first. He thereupon actuates the pushbutton switch 5 thereby establishing an energized circuit from conductor3 through conductor 4, push button switch or starting switch 5,actuating coil ii of the contactor l, stop switch 8 and conductors 9 andif to the energized conductor 2. Energization of the actuating coil 6causes the operation of the contactor l thereby closing the contactmembers El whereby a holding circuit is established for the actuatingcoil 6 through the contact members it and the starting switch 5 may bereleased.

Further, the operation of the contactor l closes the contact members I3,I 1 and i5 thereby connecting the primary winding iii to the conductorsl, 2 and 3 to thus energize the motor ll. In the particular motor shown,the primary l6 constitutes the stator whereas the rotor l8 carries thedirect current field of the motor IT.

My system of control is in this application shown in conjunction with apair of synchronous motors of like design. However, it is apparent thatsome of the novel results hereinbefore pointed out and to be pointed outfurther hereinafter may be obtained even in connection with other thansynchronous motors.

The rotor has a shaft IE! to which the load may be coupled but whichalso may carry one, or as shown a pair of bars 29 and El of magnetizablematerial of an impulse generator 23 adjustably mounted on the shaft i9by the adjusting means 2 5. The impulse generator 23 has a stator member 25 disposed adjacent the bars 20 and 2| and rigidly secured to thestator It by the securing means 26. If it be assumed that thesynchronous motor ll is driving a compressor, it will be readilyapparent that the load is of a very fluctuating character and comes to ahigh value during certain portions of the revolution or often a certainpoint during each revolution of the motor shaft. By properly positioningthe members 20 and 2f with reference to the stator 25, impulses may begenerated in the coils Ti and 28 mounted on the stator 25, whichimpulses will have a definite time relation with reference to theposition of the motor shaft it.

As heretofore explained, energization of the primary it starts thesynchronous motor H as an induction motor with the result that the alternating current induced in the field winding discharges through thedischarge circuit including contact members 29 of the field switch 30,discharge resistor El and conductor 32.

Operation of the contactor l also closes the contact members 33 therebyestablishing a cirouit from the energized conductor 4 through contactmembers conductor 34, back contact members 35 of the sequence controlrelay 36, conductor 37, actuating coil 38 of the sequence control relay3?) and conductor 48 to the energized conductor Operation of thesequence control relay 3% causes the opening of the back contact membersM which, therefore, places an open circuit in the circuit for theactuating coil 42 of the sequence control relay 3% so that this relaycannot be caused to operate once the atendant has selected motor ll asthe motor first to operate.

Operation of the sequence control relay 39 opens the contact members 43thereby placing an open circuit in one of the possible energizingcircuits for the actuating coil 64 of the field contactor G5, with theresult that the field contactor l5 cannot be energized by a circuitincluding the contact members 33. Further, the operation of sequencecontrol relay 39 causes the closing of the contact members 25 therebyclosing one por tion of the circuit including the actuating coil 41 ofthe anode energizing relay 48 adapted to control the energization of theanode Bill of the electric discharge device H5 explained more in detailhereinafter.

The operation of the sequence controlled relay 39 also causes theclosing of the contact members d9 thereof thereby establishing a closedcircuit for a portion of the circuit including the actuating coil 55 ofthe cathode energizing contactor 5|.

One additional circuit is established by the operation of the contactorI, which circuit may be traced from the energized conductor 4 throughcontact member 33, actuating coil 52 of the time limit device I2 to theenergized conductor 9. The time limit device I2 is provided with a dashpct 53 which delays the closing of the contact members 54 of the timelimit device I2 for an interval of time sufiicient in length to permitthe motor I1 to attain substantially its balanced speed, namely a speedsomewhere in the neighborhood of 95 to 98% of synchronous speed. Thetime limit device need not be of the type shown but may be any kind of aswitch having a delayed action such as an electric clock, a smallsynchronous motor, an inductive time limit relay or an ordinary clockset in operation by the operation of the contactor 1. However, theadjustment of whatever time limit device may be selected should be suchthat contact members 54 do not close prior to the time that the motor I1has attained substantially its balanced speed.

When the motor has attained its balanced speed, contact members 54 areclosed thereby establishing an energized circuit from the conductor 3through conductor 4, contact members 33 and 54, conductor 55, backcontact members 56 of the sequence control relay 36, conductor 51,actuating coil 58 of the field contactor 30 and conductor 59 to theenergized conductor I0. It is, therefore, clear that the field contactor30 is immediately energized after the closing of the contact members 54and remains energized through contact members 60. In other words,insofar as the foregoing discussion related to the starting of motor I1only, the system disclosed is a time limit control starting scheme andin and of itself and independent of the other features of the system ofmy control does not constitute part of my invention but represents asystem of control well known in the art.

Energization of the actuating coil 58 causes the operation of the fieldcontactor 30 which contactor is so designed that contact members 62 willclose before the contact members 29 open and upon deenergization contactmembers 29 will close before contact members 62 open. The closing ofcontact members 62 connects the field winding of motor 1 to the sourceof direct current by a circuit which may be traced from the positiveconductor BI through contact members 62, field rheostat 63, conductor32, one of the slip rings of the field Winding, the field winding, theother slip ring, and thence to the negative conductor 64. The fieldwinding being itself energized with direct current will cause the motorI1 to pull into synchronism and the motor will operate its load in theconventional manner.

After the motor I1 has been synchronized and is operating its load inthe desired manner and itis necessary, or found desirable, to alsoccnnect the motor I10 to the same source of alternating current and theattendant wishes to so synchronize motor I10 that it shall have itsshaft in a definite relation with reference to the shaft of motor I1,the attendant actuates the starting switch or push button I05, therebyestablishing an energizing circuit from the conductor 3 throughconductor I04, starting switch I05, actuating coil I06 of the contactorI01, stop switch I08 and conductor I09 to the conductor 40 and thence tothe energized conductor 2. Contactor I01 will close contact members I II thereby establishing a holding circuit for the actuating coil I06 andwill also close the contact members I30, I40 and I50 thereby energizingthe armatures or stator winding I60 of the motor I10.

The secondary or rotor carrying the field Winding will thus begin tooperate-operating as an induction motor-to drive the shaft I90 to whichthe load may be coupled and also drive the bars or members I20 and I2Iof magnetizable material of the impulse generator I23. The members I20and I2I may be adjustably secured to the shaft E99 by adjusting meansI24 so that the impulses generated in the windings I21 and I28 of thestator I25 of the impulse generator I 23 will have a definite positionalrelation to the shaft of the motor and thus the rotor I80. The stator IEis rigidly secured to the stator of the motor I10 by means of theconnection I26.

An alternating current will be induced in the field winding of the rotorin the well known manher and the current induced will circulate in thedischarge circuit including the contact members I29, resistor I3I andconductor I32.

The operation of the contactor I01 also closes the contact members I33thereby establishing an energizing circuit for the actuating coil I52 ofthe time limit device 3 I2 having the dash pot I 53. The time limitdevice 3I2 may be similar to the time limit device I2 and has the samefunction as time limit device I2.

The closure of the contact members I33 also establishes an energizingcircuit from the energized conductor I04 through contact members I33,conductor I16, actuating coil 50 of the cathode energizing switch 5i andcontact members 49 to the energized conductor 40. The switch 5I willthus be caused to operate, closing contact members I13, i8I and I84 andopening the contact members I82 and I823. The clostu'e of the contactmembers I13 establishes an energizing circuit from the energizedconductor I es through conductor I1I, the primary of the transformer I12and contact members I13 to conductor 40. The cathode I14 of the electricdischarge device I15 Will thus be energized immediately after theclosing of the lower contact members on the contactor I01. The cathodeI14 is connected to the negative conductor 64 of the source of directcurrent through conductor I11 and a portion of the resistor orpotentiometer I13 and conductor I19. The adjustment of the conductor I19determines the negative potential of the cathode I14.

The closing of the contact members 58! establishes a potential acrossthe resistor or potentiometer I18 by a circuit that may be traced fromthe positive conductor 83' through contact members I8i, resist-or I18and conductor 11 to the negative conductor 64. The opening of contactmembers I82 and I83 prevents energize.- tion of the portion of thesystem of control, shown in Fig. 1, that includes the electric discharge device 215.

The bias of the grid I85 with reference to the cathode I14 is determinedby the potential across conductors I19 and I85 which is, in turn,detcrmined by the potential existing between conductors I11 and I86. Thepotential of conductor I86 is, however, a function of the operation ofthe impulse generators 23 and 23. Coil 28 cf the impulse generator isconnected across the resistor I81. The circuit for this connection maybe traced from the conductor Ii'l' through resistor I81, conductor 585,back contact members i139 of the cathode energizing controlled switch25I, conductor I9I coil 28 and negative conductor 64 to the conductorI11.

Coil I28 of the impulse generator 223 on the other hand is connectedacross the resistor 281, the circuit for this connection may be tracedfrom conductor I92, conductor I93, coil I28, conductor E34, back contactmembers I05 of switch 25I, conductor I96 and resistor 281 to theconductor I92. Since the circuit between the grid I and the cathode I14includes the conductor I19, a portion of the resistor I18, a portion ofresistor I81, a portion of the resistor 281, and conductor I86, it isapparent that the bias of the grid with reference to the cathode isdetermined or influenced by the impulses generated in the coils 28 andI28. Therefore, if the members 26 and HI have a different position onthe shaft I99 with reference to the stator I25, than the positionoccupied by the members 20 and 2| on the shaft I9 with reference to thestator 25, it is apparent that when the rotors of the two machines arein exactly the same position, the impulses from the coils 28 and I28will not be in synchronism or will not occur at the same instant.Simultaneous occurrences of the impulses of the two coils will only takeplace if the rotor of one of the motors is either behind or ahead of theposition of the rotor of the other motor.

In the particular showing made in Figs. 1 and 2, the members 24] and 2i,and I20 and I2I of both the impulse generators appear to be in the sameposition on the respective shafts, but it should be noted that the fieldconnections at the slip rings are different for the two motors I1 andI13. It is, therefore, apparent that with machines of the same designand the same capacity, corresponding pole pieces of the two machineswill have opposite polarity and, even if the mentioned members weremounted on the shaft in the same relation, the rotor positions of thetwo motors would nevertheless be different during operation.

Since, as explained, the bias of the grid I85 is a function of theimpulses of both coils 28 and I28, it is readily apparent that theadjustment of the adjustable conductors shown in connection with theresistors I18, I81 and 281 may be so made that the electronic dischargedevice I15 breaks down or becomes conducting only when the impulses fromthe coils 28 and I28 occur at the same instant, namely when the voltagesof these impulse generators are additive does the discharge device l15break down.

To prevent premature operation of the electric discharge device,energization of the saturation coils 21 and I21 of the impulsegenerators 23 and 523, respectively, as well as positive energization ofthe anode 291 is delayed for an interval of time of sufiicient lengththat the motor I18 may attain its balanced speed, namely a speed of topossibly 98% of synchronous speed. This delay is accomplished by thetime delay device 3I2.

After the necessary time delay, contact members E54 are closed by thetime limit device 3I2 and in consequence actuating coil :21 of the anodeenergizing control relay 38 is energized. The circuit for this coil maybe traced from conductor Hi through contact members I5 1, actuating coil41 and contact members 45 to the energized con ductor 40. Operation ofthe relay 48 establishes a circuit from the positive conductor SIthrough adjustable resistor 2%, contact members 2%, contact members :85,conductor coil of the impulse generator I23, conductor 2&3 and coil 21of the impulse generator 23 to the negative conductor (it. The impulsegenerators 23 and I23 and the stators 25 and I25 thereof are thussuitably energized with direct current to saturate the cores of thestator in any desired manner to aid in the production of a sharperimpulse by the impulse coils 28 and I28.

Operation of the relay 48 also closes the contact members 205, therebyconnecting the anode 201 to the positive conductor 6i by a circuit thatmay be traced through the resistor 26%, contact members 265 andactuating coil 2% of the high speed field switch 268 to the anode M1.The actuating coil 266 will, however, not be energized to operate thehigh speed field switch 238 but is energized only when the dischargedevice H5 becomes conducting by reason of the concurrent action of theimpulse coils 28 and 528.

For the assumptions made, it is apparent that at this stage ofoperation, motor I1 operates as a synchronous motor whereas motor iii?operates as an asynchronous motor operating somewhere near synchronousspeed. The first instant after the operation of the time limit devicethat the rotor shaft of the two motors i1 and E10 hold the positiondesired, the impulses of the coils 28 and I28 will occur at the sametime thereby changing the bias of the grid E35 by an amount sufiioientto cause the breakdown or the discharging of electric discharge device915. When such discharge occurs, actuating coil 2% is energized and inconsequence, contact members 209 are closed thereby establishing anenergizing circuit for the field winding of the motor I10 by a circuitthat may be traced from the positive conductor 58 through contactmembers 263, field rheostat conductor the field winding and thence tothe negative conductor The high speed field switch is not designed tocontinuously carry the field current and is, therefore, provided withcontact members 'Zli for energizing the main field switch L5. Theenergizing circuit may be traced from conductor I04 through contactmembers and iii] and the actuating coil 44 01 the main field switch 45to the energized conductor iii. The main field switch 45 will thusoperate to close the contact members I62 thereby establishing a lowresist-- ance shunt for the contact members kit of the high speed fieldswitch 288. Furthermore, operation of the main field contactor or switchopens the discharge circuit for field winding at the contact membersits. A holding circuit for coil 44 is also established through contactmembers 2I I.

If the attendant wishes to start motor I18 first and thereafter wishesto synchronize motor i1 in such a manner that the motor shaft may have adefinite relation to the rotor shaft of motor i1fl, he actuates thestarting switch Hi5 thereby synchronizing motor H9 by a time limitcontrol which is effected by the time limit device (H2 in exactly themanner hereinbefore discussed in' connection with the starting of motorI1. However, in this instance the closure of the contact members I33establishes a circuit from the energized conductor Iil i through contactmembers I33, back contact members il of the sequence control relay 38which will of course, be deenergized and actuating coil to the energizedconductor Iii. The sequence control of relay 36 is, therefore, caused tooperate When motor I18 is started first with the result that time limitstarting control of motor i1 is prevented by the opening of contactmembers 56 and the closure of contact members 252 and M5 will set up thenecessary circuits for properly synchronizing motor 1 I1 in a definiterelation to the motor I19 when it is desired to start motor I1.

After the motor I18 has become properly synchronized, the attendant mayactuate the starting switch 5 and affect the starting of the mo tor I1as an induction motor exactly as hereinbefore explained. However, sincecontact members 2I5 are closed when motor I18 is already operating, acircuit is established from the energized conductor 4 through contactmembers 33, conductor 2I1, actuating coil 2I6 and contact members 2I5 tothe energized conductor II). The cathode energizingcontrol relay 25I isthus caused to operate, closing the contact members 2I8, 224 and 240 andopening the contact members I89 and I95.

The opening of contact members I89 and I disconnects certain portions ofthe control associated with the discharge device I15. Closure of contactmembers 248 merely provides a closed circuit in the portion of thiscircuit including the coils I21 and 21 of the impulse generators I23 and23, respectively.

The closure of contact members 2I8 establishes an energizing circuitfrom the conductor 4 through conductor TZZI, primary of transformer 2I9, contact members 2I8 to conductor I8, thereby causing theenergization of the cathode 220 of the electric discharge device 215from the transformer 2I9. A negative potential of a certain value isapplied to the cathode 220 by a circuit that may be traced from thenegative conductor 64 of the source of direct current through conductor226, a portion of the resistor 222 and conductor 223 to the cathode 220.The closureofcontact members 224 merely connects the potentiometer orresistor 222 across the source of direct current, namely acrossconductors 6| and 64 by a circuit including contact members 224 and thepotentiometer resistor 222 and conductor 226.

The bias of the grid 33 with reference to the cathode 220 is determinedby the potential across conductors 223 and 225 which, in turn, isdetermined by the potential across the conductors 226 and 225. Thepotential of conductor 225 with reference to the conductor 226 is,however, determined by the variations in potential caused by the coils28 and I28 of the impulse generators 23 and I23, respectively. Coil 28is connected across the resistor 221. The circuit for this connectionmay be traced from conductor 226 through conductor 64, coil 28,conductor I9I, conductor 229, contact members I82, conductor 228 andresistor 221 to the conductor 226. Coil I28 is connected across theresistor 230. The circuit for this connection may be traced fromconductor I92 through conductor I93, coil I29, conductor I94, contactmembers I83, conductor 23I and resistor 230 to the conductor I92. Byproperly adjusting the adjustable conductors on the respective resistors222, 221 and 239, the potential of the grid 233 may, of course, be soselected that discharge device 15 becomes conducting or discharges onlywhen the impulses of the coils 28 and I 28 occur at the same time. Byproperly adjusting the relative position on the shaft of the motor ofthe rotating members, of the impulse generators, it is apparent thatmotor I1 may be pulled into synchronism at any selected position withreference to the motor I10. By any position in this instance, it is, ofcourse, meant any position permitted by the design, namely the number ofpoles of the two machines.

When the impulses of the impulse generators occur at the same time,discharge device 215 becomes conducting and in consequence actuatingcoil 236 of the high speed field swith 231 is energized by a circuitthat may be traced from the positive conductor 6| through resistor 234,contact members 235, actuating coil 236. anode 238.

cathode 228, conductor 223 and a portion of the resistor 222 to thenegative conductor 64. Of course, contact members 235 would only beclosed if the time limit device I2 has operated to establish anenergizing circuit for the actuating coil 2! 3 of anode energizingcontrol relay 2I4. Furthermore, the operation of relay 2 I4 closes acircuit from the positive conductor 6I through adjustable rheostat 338,contact members 239 and 2'31), conductors 24I and 202, coil I21 of theimpulse generator I23, conductor 203 and coil 21 of the impulsegenerator 23 to the negative conductor The instant high speed fieldswitch 231 operates, contact members 34I are closed thereby establishingan energizing circuit for the main field switch by a circuit that may betraced from conductor 4 through contact members 33, 54 and 34B,actuating coil 58 of the main field switch 53 and conductor 59 to theenergized conductor 58. Gperation the main field switch 30 establishes ashunt for the contact members 242 of the high speed fieid switch 231thereby relieving these contact members of the duty of continuouslycarrying a comparatively heavy current. Further, operation of the mainfield switch 30 opens the discharge circuit in the manner hereinbeforeexplained.

The operation of the main field switch 38 of course energizes the fieldwinding of the motor l1 causes this motor to pull into synchronism insuch a manner that the shaft of motor I1 has a definite selectedrelation with reference to the shaft i9.

oi course, aware that others skilled in art, p ticularly after havinghad the benefit he teachings of my invention may devise other uitdiagrams than the particular diagram I have shown for accomplishing thenovel results of my invention. However, i do not wish to be limited tothe particular circuit diagrams shown or described but wish to belimited only by the appended claims and the pertinent prior art.

I claim as my invention:

1. In a system of control for a pair of synchronous motors, incombination, a synchronous motor having an armature winding and a fieldwinding, a source of alternating current, means for connecting thearmature to the Source of alternating current, a source of directcurrent, means for connecting the field winding to the source of directcurrent, a second synchronous motor having an armature winding and afield winding, means for connecting the armature winding of the secondmotor to the source of alternating current, a generator coupled to eachof motors and therefore driven in synchro with said motors, saidgenerators having voltage characteristics indicative of the position ofcertain points on the motor shafts with reference to correspondingplanes including the axes of the respective motors, an electricdischarge device responsive to the voltage of the said generators andthus adapted to become energized when a certain relation exists betweenthe motor shafts, and switching means responsive to said dischargedevice adapted to connect the field winding of the second motor to saidsource of direct current.

2. In a system of control for a pair of synchronous motors, incombination, a synchronous motor having an armature winding and a fieldwinding, a source of alternating current, means for connecting thearmature to the source of alternating current, a source of directcurrent,

means for connecting the field winding to the source of direct current,a second synchronous motor having an armature winding and a fieldwinding, means for connecting the armature winding, of the second motorto the source for alternating current, a generator coupled to each ofsaid motors and therefore driven in synchronism with said motors, saidgenerators having voltage characteristics indicative of the position ofcertain points on the motor shafts with reference to correspondingplanes including the axes of the respective motors, an electricdischarge device responsive to the voltage of the said generators andthus adapted to become energized when a certain relation exists betweenthe motor shafts, and switching means responsive to said dischargedevice adapted to connect the field winding of the second motor to saidsource of direct current, in synchronism with said motors, saidgenerators having voltage characteristics indicative of the position ofcertain points on the motor shafts with reference to correspondingplanes including the axes of the respective motors, means responsive toa certain combined voltage of said generators adapted to energize thefield winding of the second motor from said source of direct currentwhereby said synchronous motors are synchronized so that correspondingpoints on the motor shafts hold selected positions, at the same instant,with recference to said planes.

3. In an electrical system of control for synchronous motors, incombination, a synchronous motor having an armature winding and a fieldwinding, a source of alternating current, means for connecting saidarmature winding to said source of alternating current, a source ofdirect current, means for connecting said field winding to said sourceof direct current, an impulse generator coupled to the rotating elementof said synchronous motor, a second synchronous motor having an armaturewinding and a field winding, means for connecting the armature windingof said second synchronous motor to said source of alternating current,switching means for connecting the field winding of said secondsynchronous motor to said source of direct current, an impulse generatorcoupled to the first synchronous motor, a second impulse generator socoupled to the second synchronous motor that the impulse generatedthereby will be in electrical phase with the impulse generated by thefirst impulse generator when corresponding points on the rotatingelements of the synchronous motors are out of mechanical phase,electronic means responsive to the combined magnitude of theinelectrical-phase impulses of the impulse generators when one of saidgenerators is operated at the synchronous speed of the synchronous motorto which it is coupled and the other is operated at a speed near thesynchronous speed of the synchronous motor to which it is coupled, saidswitching means being interconnected with said electronic means andadapted to be operated in response to energization of said electronicmeans.

CHARLES C. SHUTT.

